To have a clear understanding of a situation and be confident in how to handle it; to have a good idea of what's going on.

to have no idea how things stand; to be unsure of the situation or have no confidence in how to handle a problem

Literally "mountains and valleys in the chest"; refers to having a well-thought-out plan or a clear vision for how to handle a situation before acting, originally used to describe a painter's preconceived mental preparation of a landscape.

well-versed in military strategy and tactics; used to describe someone who has great strategic wisdom despite a perhaps unimposing appearance